The process of fermentation production of a chemical product using a sugar as a raw material is utilized for production of various industrial materials. In recent years, production processes for sugars using cellulose-containing biomass that does not compete with food have been widely studied. In particular, methods using cellulase are attracting attention since such methods use less energy and cause less environmental load, while achieving high sugar yields.
Oligosaccharides have low sweetness and low calorie contents, and hardly cause dental caries. Since they have an effect of selectively promoting the growth of intestinal bacteria, a number of products are commercially available as, for example, foods for specified health uses having a function to keep favorable stomach conditions. Among these oligosaccharides, xylooligosaccharides are less susceptible to degradation by acids or digestive enzymes such as amylase and, when they are ingested by humans, they are not degraded or absorbed until they reach the large intestine. Thus, they produce their effect with a minimum effective amount of 0.2 to 0.7 g/day (Japan Confectionery and Innovative Food Ingredients Research Center; Handbook of Oligosaccharides), which is an order of magnitude smaller than those of other oligosaccharides. Xylooligosaccharides are used not only as food for humans, but also as an additive for livestock feed.
Xylooligosaccharides are produced from xylan, which is one of major constituting components of plants. Known examples of methods of producing xylooligosaccharides include a method in which pulverized hardwood is placed in circulated high temperature/high pressure water to allow hydrolytic extraction of hemicellulose in the material (JP 4557648 B), a method in which xylan is treated with xylanase produced by a Bacillus microorganism, and xylooligosaccharide is produced from the reaction filtrate (JP 61-242592 A), and a method in which a xylooligosaccharide complex contained in the reaction filtrate obtained after reaction of a chemical pulp with hemicellulase is concentrated by membrane filtration, and xylooligosaccharides are separated and recovered from the resulting concentrate (JP 3951545 B).
Xylanase is a representative enzyme used for production of xylooligosaccharides. Cellulases produced by microorganisms represented by filamentous fungi such as the genera Trichoderma, Acremonium, Streptomyces, and Aspergillus are known to have xylanase activity. On the other hand, those cellulases are known to have also β-xylosidase activity, which causes degradation of xylooligosaccharides into monosaccharide units. Thus, efficient production of xylooligosaccharides requires removal of β-xylosidase by purification of xylanase from cellulase produced by a microorganism, production of xylanase using a microorganism which does not produce β-xylosidase or the like to eliminate the influence of β-xylosidase. However, any of those methods leads to an increase in the cost of the enzyme.
As described above, xylanase is used for production of xylooligosaccharides using an enzyme. However, when cellulase having xylanase activity is used, the cellulase has not only the xylanase activity, but also β-xylosidase activity, which causes degradation of xylooligosaccharides. It has therefore been difficult to produce xylooligosaccharides using cellulase.
In view of this, it could be helpful to construct a process for simultaneous production of a sugar liquid and a xylooligosaccharide using cellulase to reduce the amount of enzyme used in the entire production process of the sugar liquid and the xylooligosaccharide, which are valuable substances, compared to the amount of enzyme used in conventional production processes in which a sugar liquid and a xylooligosaccharide are produced using separate enzymes.